Piezo electric frequency eliminator



Oct. 20, 1931. ELGREEN 1,827,843

PIEZO ELECTRIC FREQUENCY ELIMINATOR Filed March 18, 1927 INVENTOR. EKG/deg.

A TTORNEY Patented Oct. .20, 1931 eeunrrse s rai fii Pa e same ESTILL I. GREEN, or EAST ORANGE, new tensity, Assrenen r AMERICAN nutri ious V AND TELEGRAPH CQMPANY, acosrosnrron or new YORK PIEZO niii'icrnio FREQUENCY ntrrvirnsroa 7 Application file'd March 18, 1927. Serial No.'l76,546.

This invention relates to signaling systems, and particularly to arrangements in such systems for eliminating or suppressing currents of definite frequencies. f

' In signaling systems of the carrier suppression type, it is common practice to use modulators or translating devices of the pushpull type in order to balance out the carrier supply. Insuch devices the balance between ,;J the circuits is usually not perfect, so that generally some residual energy of the carrier frequency is transmitted along with side bands of the carrier frequency, these side bands corresponding to signaling currents. It has been 3 the practice heretofore to connect balancing condensers or resistances, or both, to the [translating circuits in order to produce abet ter balance, yet there was ordinarily a certain amount of; leakage of carrier current which was obviously undesirable. This leakage'of carrier current produced, inter alia, crosstalk and tones in the channels of adjoining carrier 7 systems having somewhat different frequency allocations. It, therefore, becomes apparent that it isesesntial to provide the most efficient a means to suppress this ca'rrier'current lea'k.

age.

It is therefore to provide a piezo-electric structure in con- :ro nectionwith carrier signaling systems-so that the piezo-electric structuremay act as ameans for suppressing energy of a definite frequency such, for example, as the. carrier frequency.

It is another object of this invention to provide a piezo-electric structure to supplement or even to supplant, the circuit elements heretofore employed to producebalance between duplex translating circuits, the piezo-electric energy of the carrier frequency.

It is another object of this invention to I provide a piezoelectric structure for definitely fixing the location ofthe carrier frequency so that, as energy of the carrier frequency is impressed upon thepiezo-electric structure,

there will be a high degree of absorption of the carrier frequency energy..

7 While this invention will'be pointed out I with particularity in the appended claims,

m the invention, both a'sito its furtherobjects .ielectrical properties of these-piezoelectric an object of this invention structure acting as a resonator to suppress and features will be better understood from the detailed description hereinafter following, when read in connection with the accompanying drawings, in which Figurejl represents a simple modulating system including piezo-elec'tric device for suppressing carrier frequency energy; Fig. 2 shows a duplex translating system to which a. piezo-e-lectric element is connected to supplement the balancing properties of the duplex arrangement" for the suppression ofcarrier energy; Fig. 3 shows a duplex arrangement similar to Fig.

2, in which two substantially similar piezo electric structures are employed, I one being connected to each. translating ..circuit;.,and'-' 4 shows another duplex translating system to which piezoelectric elements are con-' nected,-1nclud1ng means for inodlfying the devices. M Referring to Fig. 1 of the drawings, a

source of signals S is shown, arranged in a series circuit wlth the primary wlnding of a transformer T The transformer' T connects the source of signals to a modulatingsystem having a three-element thermionic 1 tube V, including a filament, a grid'and plate, the filament being heated .to'an.electron-emitting temperature by a localbattery.

The input circuit of the thermionic tube V circuit of the thermionic tubeV. comprises the plate and filament of the tube V, a battery B and the primary winding of the 7 transformerT the battery B providing the I necessary potential for the plate ofthisoutput circuit.

- he transformer connects the output circuit of the thermionic tube Viwith a filter H i F which may be of any well-known type,

""terminalsofthe amplifier A is another filter F which is connected to a modulating system smnlar to the one shown and described herein above. p

A plezo-electrlc device is connected between the plate and filament of the thermi- .iOHlC tube V, in shunt with the output circuit :of the tube. this system energy of the carrier frequency transmitted by the oscil- -lator O; -isimpressed upon the input circuit 10f the 'vacuumtube V along with signals voriginating in the source S T he thermionic .ftube V acts as a modulator and transmits to Its output c1rcu1t current of the carrier frequency as well as side bands of the carrier frequency corresponding to the signaling currents originating in thesource S I device Inasmuch as the gpiezo-electric is connected :across the output circuit of the thenmionicztube V and inasmuch as this devuceus arranged'to-ha've a resonant frequency approximating that of the carrier frequency, -xthe piezo-electric device will present a path I of low impedance for current ofthe carrier;

1 frequency, as compared with the impedance in the output circuit of he tube V. for current of this frequency, while at all other frequencies, the impedance of the'picro-electiic device will be very high in comparison with the impedance of the output circuitof the tube. Accordingly, the pieZo-electric device, "wall absorb substantially all ofthe energy of,

' :the carrier frequency which would otherwise -be present 1n the output circuit. and remain unsuppressed,

The very low pression of current of a definite frequency, because electncally tuned circuits winch might be employed for this purpose are in- .59.

nsiderable range of frequencies on either side herentl-y of :such high decrement that a con of the undesirable frequency are also subxstaiiti ally suppressed. .Inasmuch as the side bandsof the carrier frequency are very close :to the carrier wave in their position 1n the frequency spectrum, ordinary electrical circuits would suppress some of the ener y of :jche side band or side bands of the carrier wave as well as the energy of the carrier wave itself, and would likewise have. an undesirable effect on the output circuit impedance act the side band frequencies. 0

If it is desired to employ the piezoelectricdevice as a meansfor definitely fixing the position of the carrier wave, then it may be decrement of a piezoelectric device is particularly desirable for the supnecessary to incorporate in the oscillator 9 means for varying the frequency of oscillations sustained, so that the frequency of these oscillations may approximate within extremely narrow limits the natural vibratory period of-the piezo-electric device. On the other hand, if the frequency of oscillations sustained by the oscillator O is substantially constant normally, eans may be provided for varyingthe vibratory period of the piezoelectric device so that the vibratory period of this device mayclosely approximate the frequency of the sustained oscillations. Well known means for varying the frequency of vibration of a piezo-electric device may involve an adjustment of the distance between one or both of the electrodes of the piezoelectric device with respect to'the active faces of the device. In other words,a variationof one or both of the air gapsof the piezo-elec- .tric device may be employed to correspondingly vary the frequency of vibration of the device. l

.llig. 2 shows a source of :signalsS connected to the primary winding of the transformer T r The secondary winding of the transformer T is connected to a duplex modulating system having two three-element thermionic tubes V and Vgthe filaments of whlch areheated to electron emitting tem 'peratures by "a common battery. These tubes are preferably similar and equal in structure and characteristlcs and. mayobviously be replaced bya single duplex tube having a single filament, two gridsandtwo plates. The input circuits of these tubes are arranged in parallel with respect to the secondary Wl11(ll11gOf transformer T .WlllCll swinding is in series with battery B in the common conductor. of the input circuits of these tubes- The outputcircuits of these tubes are connected through the primary of the transformer T inpa'rallel with respect to the common plate battery B The secondary winding of the transformer T is-connected :to a filter F The filterl isconnected to-an amplifier A, and the amplifier A is. connected to the output circuit S The oscillator O which is connected :to the primary winding of the transformer T genl eratcs the carrier frequency to be employed in the system. 7 between the oscillatorO and the transformer T the grids of the devicesV and V areboth in phase with respect to the carrier frequency transmitted by the oscillator O. Oscillations :of the carrier frequency are therefore impressed in the same direction on the input circuits of these tubes; ,{The grids of these tubesare equally biased negatively by the battery B Under ideal conditions, equal currents of the carrierfrequency will also flow in the output circuits of the tubes V nd V which will beoppositely directed by the primary windings of the transformer- T so By virtue of the. connectionthat these'icurrents efiectively balance and neutralize each other. a i Y In practice, however,-it is very difficult to get two tubes which are' substantially alilre' 1n -tl1eir-structure. Nor can the two windings I f the, output=transformer which are con- :nected to the tubes be ma'deidentical in all respects. Balancing condensers of resistantes, both,are,'-accordingly in practice,

L connected'to these tubesto aidin producing'a :inore perfectly balanced condition between :the' tubesi When, for instance, the filament supply or. the plate battery. supply varies,

however, the balance'between the tubes is up :3 set and, consequently, the carrier frequency not completely suppressed. Accordingly,

a piezo-e'lectric device PE having a naturalv "vibratory period substantially equal to the period of sustainedoscillations, is connected between the platesof' the vacuum :tubes V I and V As'has been explained herein above, this piezo-electric devicefwill present a path of low impedance forenergy of the carrler frequency, and will, accordingly, efliciently suppress any of the carrierfrequencywhich quency of;oscillations sustained by the oscil lator 0. At thefrequency of thesesustained bscillatio-ns, each 'piezo-electric"device will present a pathof' extremely low impedance andfwill accordingly-prevent the transmission of currentofithis'frequency. It will-be ap'pa rent that these pie zo-electricdevices are vibrated at the same or at substantially the 2 same frequencies; "It will be alsoapparent I that these piezo-electric devices "supplement -the hitherto well-known balancing"; property "ofoppositely directed output circuitsof'a ujsh-pull system, these piezo-electricf I devices suppressing current of the 5 frequency of the sustained oscillations of carrier frequency, w'hich would 'ordinarily be transmitted be f aus'e of a ny'unbailancesin thecircuit' or cirr cuits cf the push-pull arrangement. v 5

Fig. 4 shows anarrangement 'similar to the; arrangement shown in Fig.f-3 in which suitable realctance elements are associated "wi'tl'i 'each piezoelectric devicefinorder to modify the electrical properties of each-such device: In the arrangementshown, inductive "orlcapacitatlve reactance' may be added in i serieswitheach piezo electric device; Piezoelectric devices PE and are connected betweenthe plates and filamentsofthe vac- Y uum tubes V and V5, through the reactances changed to any desired value.

the magnitude of the reactance in serieswith the piezoelectricdevice PE may be modified bythe manipulation of the switch W ,L ior/and G and through the reactances L or/and C by means of switches W andWg, respectively. 'By rotating one of-the switches, W for instance, any two of the: contacts d1, 6 f and g nay beclosed Byclosingxany pair; of these contacts, the inductance" L the capacity 0 ,01 a parallel arrangement of inductance L and capacity Ci may'ibethe magnitude of the capacity maybe adjusted to any desired value. When the/blades of switch W' close contacts c and f ftho inductance L and therapacityC are connected ina parallel circuit which is in seconnected in series with the piezoelectric? device PE When the blades of switchfWf close contacts and g ,'th'e condenser G is connected in series withthe device PE and ries with the piezo-electric" device P15 When thejcontacts d and c are closed at theswitch S ,,the inductance L is connected in series with the piezoelectric device PE and the magnitude of the'inductance may be Similarly,

By'rendering the reactance inthe circuit of the plezo-electric device 'slightlycapacitative or slightly inductive at the frequency of the oscillations sustained by thefoscillator 0, it will bejc lear thatthe impedance in the series path may be cOnsiderablylOWered,

so that this path may convenientlylshortcircuit currentofthe frequency of these "sustamed osc llat ons, Accordingly; acurrent of the frequency of the sustainedosci-llations will be substantially suppressed and, due to the sharpness of the transmission characteristic 0f the piez'o-el'e'ctric device, fthv eifectjof current'of'this frequency upon thc j side band or side bands will be negligible.

It is well to notethat the insertionfof re actance in series with a piezoelectric device modifies the region of'pos'itivereactanceex- ,hibited by the device, theregion increasing with the insertion of inductance and decreasing with the insertion of capacity. With the v insertion of inductance in series with the piezoelectric device,- not only is theregioncf positive reactance increased in width, but the maximum attainable inductive reactance is also increased and the maximum attainable capacltatlve, r'eactanceis decreased. By'the insertion of capacity in series with thefpiezo electric device, not only is the region of posi- =t1ve reactance exhibited by the piezo electric device decreasedin widthybutthe maximum attainable inductive reactance isfalso' de creased and the'm'aximum attainablecapacitative reactance is'increasedi' Obviously; the impedance in 'the'respective paths of these piezo-electric devices may be made very low at a desired frequency by theaddit'ionof these series reactance elements and. nmreoverithe i l/Nhile this invention has been shown and impedances of these paths substantially equal.

may be rendered described in certain particular arrangements merely for the purpose of illustration, it Will loe obvious that the general principles of this invention maybe applied to other and Widely varied organizations without departingfrom the spirit of the invention and the scope of the appended claims. a

hat is claimed 1s: a r 1. In a signaling system, the combination of asource of signals, a source of carrier frequency, means for modulating said carrier frequency with said signals so as to produce signals, and a plurality of piezo-electric devices shunting said modulating means vibrated at a common frequency substantially equal to the frequency of the carrier wave in order to cause its suppression. Y

2. In a carrier suppression system, the coin binati-on of a pair of three-element vacuum tubes each having an input circuit connected to its grid and cathode and an output circuit connected to its anode and cathode, a source of apair of piezo-electric devices connected in series relationship, and means for rendering their reactive values substantially equal at the frequency ofthe carrier wave.

,4- A modulatingsystem comprising a pair of translating devices, a source of high frequency energy symmetrically connected to said devices, a source of modulatingenergy oppositely connected to said devices, an out- I put circuit differentially connected to said dejyrces, and a pair of piezo-electric devices connected to'said output circuit vibrating at substantially the same frequencies.

5. 'A signaling system comprising a generatorof a high frequency wave, a source of low frequency signals, means for modulating the h gh frequency wave by the low frequency signals, and a plurality of piezo-electric devices eachhavmg a frequencyof resonance substantially the same asthe frequency of ,said generator, said piezo-electric devices being connected in series relationshipand shunting said modulating means and presentstantially equal; an unmodulated carrier Wave and side bands "of sald carrier wave corresponding tosaid.

mg a which isabsorbent to energy of the high frequency wave. V

6.The combination of a pair of vacuum tubes in push-pull .relationship,.iand a pair of substantially similar .piezo-electric devices connected f respectively Y to said vacuum tubes, said piezo-electric devices operating in synchronism.

7. The combination of a pair of space discharge devicesfliin push-pull relationship, a pair of substantially similar piezo-electric devices one connected to each space discharge device-and means for-rendering the resonant frequencies of said piezoelectric devices sub- 8. In a signaling system, a pair of mechani- "cally vibrating bodies, and a pair of reactances one in 'series (with each mechanically vibrating body, and means for rendering the impedance. of one mechanically vibrating body and the corresponding reactance substantially equalto the impedance of the other mechanically vibrating body and its corresponding reactance sothat both of said bodies may simultaneously act to suppress current of a particular frequency. 1 a

9. A pair of space discharge tubes in pushpull relationship each having an input circuit and an output circuit, a pair of piezoelectric devices one connected to each output circuit, saidpiezo-electric devices resonating at the'same frequency, said piezo-electric' devices presenting paths of low impedance in the vicinity of; the common resonant frequency. I

.10. A pair of space discharge tubes in push-pull relationship each having'an input I circuit andan output circuit, a pair of piezoelectric devices one connected in shunt with each output circuit,; the impedance of each piezo-lectric device at'aparticular frequency of vibration being low as compared to the impedanceof the output circuit to which it is connected; y. a v

i 11. The combination of a piezo-electric device of a vibratory period constant within very narrow limits, a duplex'vacuum tube'system, and an oscillator coupled to the piezoelectric device throughsaid vacuum tube system, the current of; said oscillator being varied in frequency so as to equal the vibratory frequency of the piezo-electric device, whereupon the piezo-electric device :may be rendered absorbent to the energy of said oscillator.

' 12. Ina carrier suppression system, a

source of signals, an oscillator the frequency of which may be varied as desired, a pair of three-element vacuumtubes each having an input circuit and an output-circuit, and a pairof V piezo-electric"devices each having a natural vibratory vperiod constant within exceedingly narrow limits, both of said piezoelectricdevices hav ng substantially thesame natural vibratory period, the frequency of said oscillator being varied to be substantial- 1y equal to the natural frequencyof said 'piezo-electric devices, said source of-signals and said oscillator being connected to the 5 input circuits of said vacuum tubes, each of said piezo-electric devices being connected in shunt across the output circuit of one of said vacuum tubes. r i Y 13. The combination of a pair of sources of currents of equally high frequency coupled to each other and a pair of piezo-electric devices respectively shunting said sources and naturally and independently resonant at periods corresponding to the frequency of the currents transmitted by said sources,

14. The combination of a pair ofcoupled circuits, each circuit transmitting a' plurality of frequencies, and a pair of independently operated piezoelectric devices both resonant at substantially the same period, said devices respectively shunting said circuits and suppressing currents of resonant frequencies.

15. The combination of a modulating circuit including a pair of vacuum tubes in pushpull relationship,-and a piezo-elect'ric device shunting the output circuit of said vacuum tubes, said piezo-electric device having a vibratory frequency equal to the frequency of the carrier current and substantially sup-' pressing transmitted carrier current.

In testimony whereof, I have signed my name to this specification this 17th day of March, 1927. t 5 ESTILL I. GREEN. 3 g 

